Dino-era delivery at sea

Unlike most other marine reptiles, sea snakes spend their entire lives in the water.  The sex of their offspring is determined through genetics.  Other marine reptiles, such as the sea turtles and the saltwater crocodiles, use incubation temperatures to determine offspring sex.  Chris Organ from Harvard University has traced this trait back to early reptilian ancestors from the Age of the Dinosaurs.



Organ and his colleagues have determined that this genetic trait allowed the three major groups of ancient marine reptiles to live entirely marine lives.  They constructed a family tree containing only marine reptiles with known information on how the sex of their offspring is determined.  They then expanded this tree to include other marine reptiles and birds that give live birth.  Almost all of these organisms were found to have sex chromosomes used to determine gender.  Rick Shine of the University of Sydney noted that sex chromosomes are crucial given water temperatures do not vary much, but that they are not foolproof.  For instance, when incubation temperatures are very high or low, the sex of the offspring may be the opposite of what the sex chromosome suggests.

As an aspiring marine biologist, I found this article very informative.  I was not aware that sea snakes use genetics to determine the sex of their offspring.   I also found it very interesting that sex chromosomes do not always determine the sex of offspring as I initially believed they would.  I wonder if someday ancestors of the sea turtles and saltwater crocodiles will use sex chromosomes to determine the sex of their offspring.